A snap shot of Several ships belong to the Sumud Flotilla fleeting during their journey to break the blockade on Gaza. Photo courtesy of Globle Sumud Flotilla.
"We are concerned, and that is why we will be deploying a ship to ensure that, if necessary, our citizens can be rescued and brought back to Spain," he told a new conference in New York, adding that the ship would depart on Thursday.
Italy announced earlier on Wednesday that it had sent a navy frigate to assist the flotilla.
The United Nations called Wednesday for an investigation into alleged drone attacks against a Gaza-bound aid flotilla that prompted Italy and Spain to send naval ships to help.
The Global Sumud Flotilla, carrying activists including Swedish environmentalist Greta Thunberg, blamed Israel for more than a dozen explosions heard around its vessels off Greece late on Tuesday.
UN Human Rights Office spokesperson Thameen Al-Kheetan said anyone responsible for the "violations" should be held accountable, and called for an "independent, impartial and thorough investigation".
The flotilla set sail from Barcelona this month with the aim of breaking the Israeli blockade of Gaza and delivering humanitarian aid to the territory, where the UN says civilians are starving under Israel's military offensive.
Israel, which halted two previous attempts by activists to sail to Gaza in June and July, has said it will not allow the flotilla to reach the Palestinian territory.
The flotilla's organisers accused Israel of endangering more than 500 unarmed civilians, and Thunberg labelled it a "scare tactic" that was "not going to stop us".
"We are sailing peacefully in international waters. We are not carrying weapons. We are carrying food, baby formula, medical supplies, and water," she said in an interview on the flotilla's Instagram account.
The activists said damage had been caused by "unidentified objects" dropped on deck and accused Israel of "the deployment of explosive and incendiary devices, deliberate dispersal of chemical substances onto civilian vessels".
Italy dispatched a frigate that was already in the eastern Mediterranean to provide protection for the flotilla, which is also carrying Italian activists and members of parliament.
Italian Prime Minister Giorgia Meloni condemned the drone attacks but also said the flotilla was a "dangerous, irresponsible" initiative to deliver aid that could be transported by her government in just a few hours.
Spanish Prime Minister Pedro Sánchez said Madrid would dispatch a navy ship on Thursday "to ensure that, if necessary, our citizens can be rescued".
"I want to make it clear to the government of Israel that Spain will, of course, protect its nationals, and we will do so both diplomatically and politically," he added.
The Global Sumud Flotilla currently comprises 51 vessels, with the majority located off the Greek island of Crete.
Vessels waiting to join the flotilla said they had already been targeted in two suspected drone attacks in Tunisia.
The Greek coastguard told AFP that a patrol boat from the EU borders agency Frontex was directed to the area "in response to a report of a threat" to a Polish-flagged boat, but the crew said "they did not require assistance", so it left.
The European Commission said the freedom of navigation under international law "must be upheld".
"No attacks, no drone strikes, no seizures or any use of force against the flotilla is acceptable," said commission spokesperson Eva Hrncirova.
The Sumud Flotilla describes itself as an independent group not linked to any government or political party. Sumud is Arabic for "resilience".
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